Schematic diagram illustrating the method of defining the spectral line range. For the smoothed spectrum (upper panel), the first derivative of flux with respect to wavelength is computed (lower panel). Local maxima and minima are identified where the sign of the derivative changes, marked with red upward-pointing and blue downward-pointing triangles, respectively. At certain wavelengths, distinct inflection points are observed where the derivative approaches zero without a sign change; these are indicated by green upward-pointing triangles. The wavelength range of the Hα line is thus delineated in purple, while the local pseudo-continuum is represented by the dashed black line.